The number of channels is changed in accordance with an operation mode in an image pickup apparatus. An image-pickup control unit 240 determines the number of operation channels W in accordance with an operation mode. A sensor unit 210 outputs an image pickup signal corresponding to each pixel in accordance with the number of operation channels W. A data sending unit 220 performs serial conversion on image pickup signals, and transfers them to the image processing unit 300 using a high-speed interface (a signal line 229) such as an LVDS in accordance with the number of operation channels W. A data receiving unit 311 performs parallel conversion on the transferred serial signal for each of the channels in units of M bits. A data reconstruction unit 500 detects a synchronization code embedded in the parallel signals, extracts data windows, and supplies, to a signal line 319, image pickup signals of bit length n which are reconstructed from the data windows. A clock gating circuit 330 supplies a clock CLK3 to a signal line 337 only during a period in which a valid flag (a signal line 316) indicates validity.